Wall-mounted fluid-fuel furnace

ABSTRACT

A gas or other fluid fired furnace for mounting in a wall, especially of a recreational vehicle providing living accommodations, such as so-called &#39;&#39;&#39;&#39;campers,&#39;&#39;&#39;&#39; house trailers, and the like, where space is at a premium and special problems of vibration, proper venting, and reliability in operation are presented. An elongate, specially fabricated, Venturi-tube burner is mounted, along with a fuel feed control unit, on a removable closure plate positioned across the lower end of a front pan-like member of a shallow, rectangular, upstanding firebox. The firebox provides a combustion chamber and heat exchanger for the furnace in a compact heater unit housing and has an outwardly extending peripheral fin through which a fuel supply extends at the bottom of the firebox and is preferably canted forwardly along the top of the firebox to direct air flow and increase efficiency. A special vent unit, provided for mounting exteriorly of the spaced to be heated flush with the exterior wall face and having a lower air inlet separated from an upper gas outlet by baffles, is connected with the heater unit by air or gas flow conduits which are thermally isolated one from the other by special gasket and mounting arrangements.

United States Patent Jackson 51 May 16, 1972 [s41 WALL-MOUNTED FLUID-FUEL FURNACE [72] Inventor: George W; Jackson, Salt Lake City, Utah [73] Assignee: Hydro Flame Corporation, Salt Lake City,

Utah

[22] Filed: July 16, 1970 [21] Appl. No.: 55,378

7 Related US. Application Data [63] Continuation-in-part of Ser. No. 825,189, May 16,

1969, abandoned.

[52] US. Cl. ..126/85 B, 126/116 B, 126/307 R [51] 1nt. Cl ..F23l l/00, F24h 3/02 [58] Field of Search ..126/85, 85 B, 90, 110, 110 B,

[56] References Cited UNITED STATES PATENTS 2,411,313 11/1946 Zimbelman et al ..126/85 2,198,535 4/1940 James ....l26/3l4 2,632,435 3/1953 Lundstrum ..126/85 B UX 2,964,034 12/1960 Nordholt et al. ,....126/85 B X 3,017,878 1/1962 Cayot ..126/85 B X 3,168,091 2/1965 Jacks0n.. ..126/85 B X 3,171,402 3/1965 Carlson.-..... ...l26/307 X 3,199,504 8/1965 Morin,'.lr. et al.. ..126/85 B X 3,348,533 10/1967 Wilhoite ..126/85 B X FOREIGN PATENTS OR APPLICATIONS 1,018,398 1/1966 Great Britain ..126/314 Primary Examiner-Charles J. Myhre Attorney-Mallinckrodt & Cornaby [57] ABSTRACT A gas or other fluid fired furnace for mounting in a wall, especially of a recreational vehicle providing living accommodations, such as so-called campers," house trailers, and the like, where space is at a premium and special problems of vibration, proper venting, and reliability in operation are presented. An elongate, specially fabricated, Venturi-tube burner is mounted, along with a fuel feed control unit, on a removable closure plate positioned across the lower end of a front panlike member of a shallow, rectangular, upstanding firebox. The firebox provides a combustion chamber and heat exchanger for the furnace in a compact heater unit housing and has an outwardly extending peripheral fin through which a fuel supply extendsat the bottom of the firebox and is preferably canted forwardly along the top of the firebox to direct air flow and increase efficiency. A special vent unit, provided for mounting exteriorly of the spaced to be heated flush with the exterior wall face and having a lower air inlet separated from an upper gas outlet by baffles, is connected with the heater unit by air or gas flow conduits which are thermally isolated one from the other by special gasket and mounting arrangements.

13 Claims, 10 Drawing Figures WALL-MOUNTED FLUID-FUEL FURNACE RELATED APPLICATIONS This application is a continuation-in-part of a copending original application Ser. No. 825,189 filed by me May 16, l969, now abandoned.

BACKGROUND OF THE INVENTION 1. Field The invention is in the general field of small fluid-fired furnaces having compact heater units for space heating and having vent units for both drawing in combustion air and discharging combustion gases exteriorly of the space to be heated, especially in a vehicle.

7 State of the Art Popularity of mobile homes'and of recreational vehicles, such as campers" carried in the beds of conventional pick-up trucks, house trailers, and specially built automobiles'of various types providing living space therein, has prompted the development of small, wall-mounted furnaces fired by gas supplied from so-called LPG," liquified petroleum gas, cylinders. A typical furnace of this type is shown in US. Pat. No. 3,168,09l granted Feb. 2, 1965. Although furnaces of this design and construction have been generally satisfactory, it has been recognized that improvements in efficiency, reliability, and durability would be desirable.

Objectives This invention was made to improve the performance of wall furnaces of this type, without increasing size, and to minimize breakdowns due to the inevitable jolting and vibration resulting even from travel over smooth roads.

SUMMARY OF THE INVENTION In the accomplishment of the objectives of this invention, a Venturi-type burner of unique design is combined in a unique manner with a special firebox that provides a combustion chamber and heat exchanger for the furnace. The firebox is formed as a fluid-tight rectangular housing having opposite broad panel walls and relatively narrow peripheral walls and provided with conduits for drawing in combustion-supporting air and for exhausting gaseous products of combustion by way of a special vent unit open to the atmosphere exteriorly of the space to be heated.

The burner utilizes standard controls for supplying thegas and is constructed for compactness by turning a Venturi fuelair mixing portion back under the burner proper. A unique feature of the burner is its fabrication from a pair of metal stampings, each provided with a longitudinally extending series of circular gas jet orificesvof varying sizes and the pair being secured together in face-to-face, fluid-tight relationship. The burner and controls therefor are advantageously mounted on the inside face of a plate that fits over a front access opening at the bottom of the firebox.

The firebox is constructed of a pair of shallow, pan-like metal stampings with outwardly extending rims and preferably having transverse corrugations pressed into their broad panel walls, the corrugations of one panel wall being located in mating relationship with those of the opposite panel wall immediately above the burner for increasing rigidity as well as for fiame-baffling purposes. These pan-like members are placed in open'face to open-face relationship and are sealed together at and along their rims, as by seam welding, so as to form a combustion chamber with the flame-baffling corrugations located with respect to each other as indicated above. The access opening is provided along the lower end of the front pan-like member and is closed by the plate that carries the burner and controls. A fuel supply pipe for the burner is accommodated by receiving recesses found in confronting portions of the rims of the front and rear pan-like members.

The firebox as so formed is'mounted within a louvered housing to form a heater unit that provides for the inflow of cool air to be heated and for the outflow of such air after passing over the heat-exchanger walls of the firebox. The peripheral fins of the firebox provided by the outwardly extending rims of the pan-like members is preferably canted forwardly along the top of the firebox to direct air flow and increase efficiency.

Inlet conduits for combustion supporting air and for exhaust of combustion gases are connected to the rear panel wall of the firebox and pass through both the heater unit housing and the wall of the structure in which the furnace is mounted. Passage of the exhaust conduit through the wall of the heater unit housing is supported and sealed by a special gasket arrangement. A special vent unit for the control of inflow of combustion air and for the outflow of gases of combustion is connected to such conduits at the opposite set of ends thereof so as to be located exteriorly of the structure in which the furnace is placed, flush with an exterior wall face.

THE DRAWINGS There is shown in the accompanying drawings a gas furnace construction that is presently contemplated as the best mode of applying the invention in actual practice.

In the drawings:

FIG. I is a view in front elevation of the furnace as adapted for installation in a wall of living space in a vehicle, much of the decorative and protective louver at the front of the heater unit being broken away to reveal interior parts;

FIG. 2, a top plan view, intermediate parts of the conduits between heater unit and vent unit being broken out for convenience of illustration;

FIG. 3, a longitudinal vertical section taken along the line 3-3 of FIGS. 1 and 2 and drawn to a somewhat larger scale;

F IG. 3A, a fragmentary vertical section taken along the line 3A-3A of FIG. 3;

FIG. 4, a transverse horizontal section taken along the line 4-4 of FIG. 1 and drawn to a somewhat larger scale;

. FIG. 5, a fragmentary vertical section taken along the line 5-5 of FIG. 3 to show the Venturi burner in front elevation;

FIG. 6, a fragmentary horizontal section taken along the line 6-6 of FIG. 3 to show the Venturi burner in top plan;

FIG. 7, a fragmentary horizontal section taken along the line 77 of FIG. 5 and drawn to a larger scale;

FIG. 8, a vertical section taken along the line 8-8 of FIG. 3 to show the interior of the vent unit in elevation; and

FIG. 8A, an end elevation of the heater unit and its rearwardly-extending conduit sections as viewed from the line 8A8A FIG. 3.

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENT In the specific construction illustrated, the furnace is adapted to be mounted in and through a wall of the living space to be heated in a recreational vehicle or mobile dwelling. As shown in FIGS. 2 and 3, a heater unit 10 is connected with a vent unit 11 by means of an assembly 12 of flow conduits.

The heater unit 10 includes a gas-tight firebox 13 of rectangular formation having opposite broad panel walls and relatively narrow peripheral walls 13b. The firebox is fabricated from two similar, shallow, pan-like metal stampings 14 with out-turned rims 14a and transverse mating corrugations 14b. Such stampings are placed together in open-face to open-face relationship with the corrugations 14b in mating placement immediately above the burner, as shown, for flamebaffling purposes, and are sealed, fluid-tight, about their rims as by means of scam welding. The rims and resulting peripheral fins are canted forwardly, as at 140, FIG. 3 (also FIG. 4), along the top of the firebox to direct air flow and increase efficiency, thereby contributing significantly to .the compactness of the furnace.

An access opening 15, FIG. 6, leading into the interior of firebox 13 is provided in the front panel wall 13a at the lower end thereof and is normally closed tightly by a plate 16, that is held in place by screws (not shown). Such plate 16 has a dependent flange 16a corresponding to the rims 144. A gas burner 17 is mounted on the inside face of such closure plate 16, as is also a conventional pilot light burner 18. A gas supply pipe 19 projects downwardly from connection with the burner 17 and passes through a receiving opening in the bottom of the firebox formed by corresponding recesses 14c and 16b in the rim and flange 160, respectively, see FIGS. 3 and 5, to connection with a conventional gas-feed control unit 20. A saddle plate 21 welded to pipe 19, secures such pipe to the flange 16a of closure plate 16 at recess 16b, such saddle plate being welded to flange 16a.

The burner 17 is elongate, and has a gas-air mixing, Venturi portion 17a turned back under an elongate, burner proper 17b. Pipe 19 connects to the burner at the end of such turnedback portion 17a, and a fine jet of fuel is discharged from a jet nozzle 22, FIG. 7, through an air gap 23, where it entrains air, and into the throat of Venturi tube 24. The gas-air fuel mixture rounds bend 170 of the burner and flows along the length of the burner proper 17b, emerging through orifices 25. These preferably vary in size along the length of such burner proper to provide for substantially uniform distribution of the fuel mixture. Size variations are empirically determined for any particular furnace design by observation of the burning characteristics and altering the size of any given hole or holes when yellow flames are observed rather than the more desirable smoke-free blue flames. An additional orifice 25a near the pilot light aids in igniting the burner.

Burner 17 is fabricated from a pair of metal stampings, indicated by 17b and 17c in FIG. 6, which have out-turned rims 17d and are welded together, fluid-tight, in face-to-face relationship. The gas jet orifices are stamped out in double rows in the respective stampings at opposite sides of the rims 17d and directed upwardly and outwardly toward the walls of the firebox, see FIG. 3.

Back of burner 17 in the back panel wall of the firebox, a pair of air-flow tubes 26 carry air from a plenum chamber 27, FIG. 3, into the interior ofthe firebox at the level of burner 17. A baffle plate 28 across the upper portion of such tubes insures delivery of air below the level ofthe burner orifices.

An exhaust conduit or flue 29 communicates with the interior of the firebox through the back panel wall 13:: thereof above corrugations, i.e. baffles, 14b, and extends backwardly through plenum chamber 27 to connection with vent unit 11. It should be noted that the corrugations or baffles 14b preferably occupy the entire panel wall expanse between low level conduits 26 and upper level conduit or flue 29.

Firebox l3 and control unit 20 are mounted within a housing 30, which defines flow channels 31, FIG. 3, about the heat exchanger walls of such firebox for air to be heated. A louvered front 32 for the housing is attached to sheet metal bottom wall 30a, as by screw 33, and, by means ofa tongue and groove arrangement 32a, to a radiation flap 30c cut from top wall 30d. A first radiation shield 34, FIG. 1, is attached to firebox 13, as by means of mounting brackets 34a, and a second radiation shield 35 is riveted to the first at dimples 35a. A third radiation shield 35-1 is interposed between the first two. These radiation shields and the walls of housing 30 define an air-flow passage 36. Rear wall 30c of the housing, it should be noted, forms the front wall of plenum chamber 27.

A small electric fan and controls therefore 37, FIG. 1, are mounted in the lower part of housing 30 next to gas control 20. The lower part 32b, FIG. 3, of louvered front 32 may be formed as a conveniently removable door to provide access to the controls.

The fan draws cool air in through louvers 32b and forces it to flow upwardly about the heat exchanger walls of firebox l3 and through air-flow channels 36 and 31 and out louvers 32 along the upper part of housing 30. Radiant heat passes through louvers 32 from front panel wall 13a.

Exhaust conduit or flue 29 runs through protective tubes 38 and 38a, and the conduit 39 discharge into plenum chamber 27.

Vent unit 1 1 is formed as a rectangular, pan-like housing 40 with a louvered front 40a. Flue 29, tube 380, and conduit 39 communicate with the interior of housing 40 through its back wall 40b, An exhaust vent pan 41 is carried within housing 40 by the discharge end offlue 29. It has side walls 41a, upwardly sloping top wall 41b, a partial front wall 41c immediately behind louvered front 40a, an open bottom 41d, and a back wall 4le. Front wall 41c leaves an upper, discharge opening 42 extending across the width of such exhaust pan. Behind such discharge opening and extending below the upper end of front wall 41c is an exhaust baffle 43.

Exhaust vent pan 41 and baffle 43 are advantageously constructed as a unit attached to the end of the adjacent section of exhaust flue 29, so that all of these parts are easily assembled by merely pushing them into place as such flue section is telescoped into the other flue section, see FIG. 3. The position of such unit relative to housing 40 is securely fixed by tongues 41f pushed into receiving recesses of respective mounting brackets 41g, FIG. 8.

Flue gases discharge from the upper part of exhaust vent pan 41 and through exhaust baffle 43 and out to the atmosphere through the upper part of louver 40a. Combustion air enters housing 40 and conduit 39 through the lower part of louver 40a. An entry passage 44 for air to flow into the space between exhaust flue 29 and tube 38a is provided opposite the louvered lower open front of the vent unit. A rectangular heat shield 40d is provided as a part of housing 40 for direct installation in an exterior wall of the structure to be heated by the furnace, so that the flanges 40c of housing 40 will be substantially flush with the exterior face ofsuch wall.

It is important that there be a minimum, if any, transfer of heat from exhaust flue 29 to its surrounding air-flow conduits and to housing 30. To this end, a specially fabricated, flue-supporting seal 45 is provided between exhaust flue 29 and rear wall 30:: of heater housing 30. By use of this seal, it is possible to increase heat output per unit time without altering compactness of the furnace and without causing a fire hazard.

The seal 45, see especially FIG. 3A, comprises a recessed retainer frame 46, advantageously in the form of a metal stamping, positioned against and secured tightly to the back face of heater housing rear wall 302 as by means of welding. Within recessed portion 46a of frame 46 is a sheet or plate of stiffly flexible, heat-resistant gasket material 47 having a central receiving opening for flue 29, whose diameter is somewhat less than the outside diameter of such flue so as to make a fluid-tight connection when the flue is pressed through the receiving opening. Frame 46 has a central opening 46b whose diameter is sufficiently larger than the outside diameter of the flue to insure that there is no contact between flue and plate when the former is installed in the seal 45. Heater housing rear wall 30c is correspondingly apertured at 48, FIG. 3, for the same purpose.

Support for radiation protective tube 38 is provided at seal 45 by brackets 49, FIG. 3A, which are advantageously stamped out of the metal blank from which retainer frame 46 is stamped. The joinder between the end of tube 38 and its interconnected tube 38a preferably has considerable tolerance, as indicated at 50, to simplify assembly of vent unit 11 with heater unit 10. Support for the tube 38a near its interconnection with tube 38 is provided by brackets 51, FIG. 8A, and support for the opposite end of tube 38a is provided by brackets 52, FIG. 8, secured to such tube 380 and to housing 40.

Gasket 47 is smaller in extent than is the recess of recessed portion 46a (see the dotted line representation in FIG. 3A) to afford leeway for lateral expansion and contraction under changing thermal conditions. Such gasket is preferably made by cutting or stamping to required configuration a steel-wirereinforced, pressed asbestos board obtainable on the open market.

It should be noted that the unique arrangement of pan-like members 14 and closure plate 16, with burner 17, control unit 20, and fuel supply pipe 19 carried by such closure plate, not only makes for ease and economy of fabrication during the manufacturing stages but enables important operating parts of the furnace to be conveniently removed as a single entity for repair purposes if and when required. All that is necessary for this is to unscrew the attachment screws holding closure plate 16 in place and to disconnect control unit 20 at 20a from the gas line (not shown).

Although the specific construction illustrated is presently preferred and is contemplated as being the best mode of applying the invention in practice, there are various ways in which the broader inventive concepts taught here can be carried out. 7

I claim:

1. A fluid-fired furnace adapted to be mounted on a wall of a structure to be heated, comprising a heater unitincluding a substantially rectangular heat exchanger firebox having front and rear broad panel walls and relatively narrow peripheral walls defining an. upstanding combustion chamber, said firebox being formed by similar front and rear pan-like members having outwardly-turned rims and being secured together in open face to open face relationship to provide an intermediate peripheral fin extending outwardly of such firebox to increase the heat exchange surface area thereof; an elongate fluid fuel burner extending substantially entirely across the lower end of said firebox to direct flames upwardly in said combustion chamber across the width thereof; conduit means communicating with the interior of the firebox at a low level thereof through the rear panel wall for supplying combustionsupporting air to said burner; conduit means communicating with the interior of the firebox at an upper level thereof for exhausting gaseous products of combustion from the firebox; a housing having walls defining flow channels about the exterior of said firebox for air to be heated and providing for inflow of cool air and outflow of heated air; the lower end of the front panel wall of the firebox and the adjacent bottom peripheral wall portion of the corresponding pan-like member being provided with an access opening leading to the interior of the firebox; a closure plate for said opening provided with a depending flange corresponding to the confronting portion of the rim of the rear pan-like member, the burner being mounted on the inside face of said closure plate; and a fluid fuel supply pipe leading into the firebox from the exterior thereof and connected with said burner, the rim of the rear pan-like member and the flange of the closure plate being recessed for receiving and accommodating said pipe.

2. A furnace according to claim 1, additionally including a saddle plate secured to the fuel supply pipe and to the inner face of the depending flange of the closure plate.

3. A furnace according to claim 1, wherein a control unit for feeding fluid fuel to the burner is connected to the supply pipe below the firebox within the flow-channel-defining walls.

4. A furnace according to claim 1, wherein the broad panel walls of the firebox in the areas thereof immediately above the burner and between the low level and upper level conduits are transversely corrugated, respectively, in mutually spaced relationship across the interior of said firebox, said corrugations being in approximately mating positional relationship with respect to the placement of ridges and valleys to provide flame-diverting baffles immediately above the burner.

5. A furnace according to claim 1, wherein the peripheral fin of the firebox is canted forwardly along the top of the firebox to direct air flow.

6 A furnace according to claim 1, additionally including a vent unit for drawing in combustion-supporting air from, and for exhausting combustion gases to, the atmosphere while the structure to be heated is traveling along a highway, said vent unit having bafile means separating a gas-exhaust area from an air-intake area, the low level conduit means communicating and holding a sheet of stiffly flexible, heat resistant, sealing material with freedom for lateral movement, said flue passing snugly through said sheet of sealing material and through said wall in spaced relationship with said wall and said retainer frame.

7. A furnace according to claim 6, wherein the exhaust flue extends to interconnection with the vent unit through a radiation protective conduit supported at one end by brackets affixed to the retainer plate of the seal and at the opposite end by brackets affixed to the vent unit.

8. A furnace according to claim 7, wherein the vent unit includes a housing adapted to be mounted in the wall of the space to be heated, and the baffle means includes an exhaust vent pan having a baffle thereon defining exhaust openings near the top and being open at the bottom for the inflow of atmospheric air, said vent pan being secured to the exhaust flue and removably secured to the vent unit housing.

9. A furnace according to claim 8, wherein the vent pan is removably secured to the vent unit housing by means of tongues at opposite sides of the vent pan frictionally fitted into receiving recesses of mounting brackets secured to the vent unit housing.

10. A furnace according to claim 1, wherein the burner is fabricated from two recessed metal stampings having outwardly extending peripheral rims and welded together in open face to open face relationship to provide an intermediate peripheral fin, there being a series of burner openings extending longitudinally of each of said metal stampings to one side of said fin and canted outwardly toward the broad panel walls of the firebox.

11. A furnace according to claim 1, wherein the housing defining flow channels about the exterior of the firebox includes top, bottom, side and rear walls, an internal first heat radiation shield attached to the firebox and defining flow channels therearound, a second heat radiation shield defining flow channels around the said first shield, and a third heat radiation shield interposed between said first and said second shields, the said top wall being cut and bent upwardly as a flap to form another heat radiation shield extending along the width of the housing.

12. A furnace according to claim 11, wherein the first and second radiation shields and said second radiation shield and the flap of the top wall of the housing are connected by dimpled portions of said second radiation shield.

13. In a fluid-fired furnace adapted to be mounted on a wall of a structure to be heated and comprising a heater unit, provided with a heat exchanger firebox having front and rear broad panel walls and with a housing having walls defining flow channels about the exterior of said firebox, a vent unit for exhausting combustion gases to the atmosphere from said firebox, and an exhaust flue interconnecting said firebox and said vent unit and passing through a wall of said housing, the provision of a fluid-tight, heat resistant seal supporting said flue in its passage through the housing wall, said seal including a retainer frame secured to said wall; and a sheet of stiffly flexible, heat resistant, gasket material held by said frame with freedom of movement within said frame as an entire sheet and peripherally thereof substantially without distortion, said flue passing snugly through said sheet and through said wall in spaced relationship with said wall and said retainer frame. 

1. A fluid-fired furnace adapted to be mounted on a wall of a structure to be heated, comprising a heater unit including a substantially rectangular heat exchanger firebox having front and rear broad panel walls and relatively narrow peripheral walls defining an upstanding combustion chamber, said firebox being formed by similar front and rear pan-like members having outwardly-turned rims and being secured together in open face to open face relationship to provide an intermediate peripheral fin extending outwardly of such firebox to increase the heat exchange surface area thereof; an elongate fluid fuel burner extending substantially entirely across the lower end of said firebox to direct flames upwardly in Said combustion chamber across the width thereof; conduit means communicating with the interior of the firebox at a low level thereof through the rear panel wall for supplying combustion-supporting air to said burner; conduit means communicating with the interior of the firebox at an upper level thereof for exhausting gaseous products of combustion from the firebox; a housing having walls defining flow channels about the exterior of said firebox for air to be heated and providing for inflow of cool air and outflow of heated air; the lower end of the front panel wall of the firebox and the adjacent bottom peripheral wall portion of the corresponding pan-like member being provided with an access opening leading to the interior of the firebox; a closure plate for said opening provided with a depending flange corresponding to the confronting portion of the rim of the rear pan-like member, the burner being mounted on the inside face of said closure plate; and a fluid fuel supply pipe leading into the firebox from the exterior thereof and connected with said burner, the rim of the rear pan-like member and the flange of the closure plate being recessed for receiving and accommodating said pipe.
 2. A furnace according to claim 1, additionally including a saddle plate secured to the fuel supply pipe and to the inner face of the depending flange of the closure plate.
 3. A furnace according to claim 1, wherein a control unit for feeding fluid fuel to the burner is connected to the supply pipe below the firebox within the flow-channel-defining walls.
 4. A furnace according to claim 1, wherein the broad panel walls of the firebox in the areas thereof immediately above the burner and between the low level and upper level conduits are transversely corrugated, respectively, in mutually spaced relationship across the interior of said firebox, said corrugations being in approximately mating positional relationship with respect to the placement of ridges and valleys to provide flame-diverting baffles immediately above the burner.
 5. A furnace according to claim 1, wherein the peripheral fin of the firebox is canted forwardly along the top of the firebox to direct air flow.
 6. A furnace according to claim 1, additionally including a vent unit for drawing in combustion-supporting air from, and for exhausting combustion gases to, the atmosphere while the structure to be heated is traveling along a highway, said vent unit having baffle means separating a gas-exhaust area from an air-intake area, the low level conduit means communicating with said air-intake area and the upper level conduit means comprising an exhaust flue communicating with said gas-exhaust area and passing through a wall of the flow-channel-providing housing; and a fluid-tight, heat resistant seal supporting said flue in its passage through the housing wall, said seal including a recessed retainer frame secured to said wall and holding a sheet of stiffly flexible, heat resistant, sealing material with freedom for lateral movement, said flue passing snugly through said sheet of sealing material and through said wall in spaced relationship with said wall and said retainer frame.
 7. A furnace according to claim 6, wherein the exhaust flue extends to interconnection with the vent unit through a radiation protective conduit supported at one end by brackets affixed to the retainer plate of the seal and at the opposite end by brackets affixed to the vent unit.
 8. A furnace according to claim 7, wherein the vent unit includes a housing adapted to be mounted in the wall of the space to be heated, and the baffle means includes an exhaust vent pan having a baffle thereon defining exhaust openings near the top and being open at the bottom for the inflow of atmospheric air, said vent pan being secured to the exhaust flue and removably secured to the vent unit housing.
 9. A furnace according to claim 8, wherein the vent pan is removably secured to the vent unit housing by means of tongues at opposite sides of the vent pan fricTionally fitted into receiving recesses of mounting brackets secured to the vent unit housing.
 10. A furnace according to claim 1, wherein the burner is fabricated from two recessed metal stampings having outwardly extending peripheral rims and welded together in open face to open face relationship to provide an intermediate peripheral fin, there being a series of burner openings extending longitudinally of each of said metal stampings to one side of said fin and canted outwardly toward the broad panel walls of the firebox.
 11. A furnace according to claim 1, wherein the housing defining flow channels about the exterior of the firebox includes top, bottom, side and rear walls, an internal first heat radiation shield attached to the firebox and defining flow channels therearound, a second heat radiation shield defining flow channels around the said first shield, and a third heat radiation shield interposed between said first and said second shields, the said top wall being cut and bent upwardly as a flap to form another heat radiation shield extending along the width of the housing.
 12. A furnace according to claim 11, wherein the first and second radiation shields and said second radiation shield and the flap of the top wall of the housing are connected by dimpled portions of said second radiation shield.
 13. In a fluid-fired furnace adapted to be mounted on a wall of a structure to be heated and comprising a heater unit, provided with a heat exchanger firebox having front and rear broad panel walls and with a housing having walls defining flow channels about the exterior of said firebox, a vent unit for exhausting combustion gases to the atmosphere from said firebox, and an exhaust flue interconnecting said firebox and said vent unit and passing through a wall of said housing, the provision of a fluid-tight, heat resistant seal supporting said flue in its passage through the housing wall, said seal including a retainer frame secured to said wall; and a sheet of stiffly flexible, heat resistant, gasket material held by said frame with freedom of movement within said frame as an entire sheet and peripherally thereof substantially without distortion, said flue passing snugly through said sheet and through said wall in spaced relationship with said wall and said retainer frame. 